Dividing ornamental grasses is easy and rewarding, but it takes a lot of strength, especially for older large plants. Spring, when plants are beginning growth, is the best time to do division. Dividing in summer or fall can be done, but plants should have a minimum of one month good growing conditions before winter.
Plants that have dead centers respond well after division. Bunch grasses, such as these large miscanthus, tend to die in the center as the growing points are compressed and crowded. The dead center is often only visible in the spring. By summer, the plants are large and thick and you cannot see the dead center.
Some grasses decline with age and may become shorter or stop growing. Division can also rejuvenate these older plants. Grasses that were in the sun but may be shaded by growing trees, can also be invigorated by division and placing them in full sun.
Is it very possible to grow large ornamental grasses for 10-20 years and not do any division. If plants are sited in the good growing conditions, they can be self sustaining, long lived perennials with no need for division.
The following slideshow highlights dividing tufted harigrass, Deschampsia caespitosa. As the botanical name indicated, this is a caespitose or bunch grass. Division in the spring allows you to see what portions are dead and which are alive. The older the clump, the more chance for portions of it to die. However, there is often enough alive to create a good landscape plant.
Guidelines to use in division of grasses:
- The older the plant, the more difficult it will be to cut into the hard woody center of the crown. Here is where strength and sharp tools are needed.
- Dig and divide when plants are showing new growth in the spring, then you can tell what portions are dead or alive.
- Determine where you will place new divisions and prepare the planting holes before you dig up the original plant.
- Use a sharp spade or shovel or a sharp kitchen knife to cut the original plant into sections
- Each small root/shoot crown section or stem and root piece, will potentially become a new plant; a minimum of 10 stems or 10 root/shoots should be kept on each division for best success.
- If possible cut a section out of a clump rather than removing the entire plant, especially if you want a portion to remain in the same location. If moving the plants to a new location, dig a circle around the plant and remove it from the original location. Cut into 4-6 sections, keeping as much root and stem as possible.
- If plants are not vigorous and growth is lopsided in the spring, division is a good idea: divide and discard any dead portions
Depending on the size of division, grasses recover from division in 1-3 years. Additional water, even for plants that prefer dry sites is necessary for the first few weeks of establishment after division.